I am working on some unmanned vehicles and it is required to have both video and telemetry transmissions. I would first want to look for some modules that are capable of sending both of telemetry data and video link. Do you have any suggestions for this? By the way it is necessary to have these modules ranges to be at least 10km in LOS (preferably better).
Please read the other thread linked. They proved channel interference in the same band can be avoided. Most modern radios are spread spectrum and auto hopping such that they avoid interference automatically. Unless you just jam a fat broadband noise down the range, there is still space for your channel. Thus, what I'm saying is don't rule it out 2.4 until you have done actual real world testing.
I'm not quite sure yet why I would need an extra uplink as well as i could just use the 2.4GHz for that, couldn't I?
I don't know how much you have messed with the project but you want RF telemetry to connect to Mission Planner at the PC and be able to tune, set waypoints, moniter status, get logs, etc... I cannot stress how important that link is and it can act as a backup channel for joystick control. Not to mention, for any commercial use of a UAV, a backup control link is a requirement, not an option. That only makes common sense since 10km is further than visual range. How else are you going to have a remote kill switch? FPV camera and the information provided by an OSD is often not enough. That's why guys are adding features to the OSD but at some point how crowded can that screen get?
Next point. Wouldn't it be nice to get a clean, non-OSD overlayed video image to the ground station and then add OSD info at the groudn station to a specific video split on the screen you want to see OSD info on? I say this because the flipside is, if OSD is added at the machine across the only video link, you cannot strip it off at the ground station.
You have mutliple problems in front of you and yes, I realise it's not quite as bad as an aircraft, because you are building a ground vehicle. The point is, at 10km you want a control channel, not a channel full of video feed (your idea of shoving mpeg down the telemtry link) which won't work anyway. The bandwidth isn't high enough and I don't know how you would mux the data.
There is not enough bandwith for control, video, and telemetry, down any one single feed or radio. It will be a compromise and not a good one.
I say that you want a constant feed of telemetry back because of the DARPA challenge.
The one thing I took away was that on the ground, you have 10 times more problems with obstacle ovoidance, but also, things like tip-over, ruts and holes to get stuck in, traction problems. What abut the vehicle that cought fire because it spun the tires stuck on a rock until the whole machine was lost. The only way you know is telemtry and you have to go the extra mile with axle and wheel and pressure sensors to determine if the vehicle is stuck, what wheel has traction, etc. How else from field testing are you going to be able to tune your obstacle avoidance? If every time it get's stuck, you have to go 10km, get the thing, bring it back and download a log and "hope" you can figure out the failure, that radio telemetry link is going to start looking very attractive.
thanks again for your help. I'm not quite sure though why you now think I wanted to build a ground vehicle, i can't remember having said such thing, infact I said quadrocopter in my last post^^.
Also I never said I wanted to use OSD, it was always my intention to send down Video and Telemetry in different channels and then overlay them in the groundstation, however what i wanted to avoid is having 2 TX on my quadrocopter as it will drain batteries etc etc.
But I get more and more to the point that video transmission is not possible over the 3DR kit and that i need the 3DR kit for telemetry so i will need 2 TX the one way or the other. The other thread you linked only stated that 900MHz could be used together with 915MHz so 15MHz difference is enough, hopefully its the same case for 2.4GHz
Sorry for that confusion about vehicles. Point being, it all that much more valid for a Heli flying 10km away.
I think you are looking at labels rather than specs. In other words, the generic 900MHz video TX is not center lobed on 900MHz, neither is the 915MHz 3DR radio. It's spread spectrum over a wide range, with complicated signal encoding. By design, the signal is made to reject normal interference from co-channels (adjacent or overlaping frequency). It would tak a book just to cover the basics here but it's not like the old days of RC where 72 or 75MHz narrow band frequency channels were absolutes. This is why you can have generic 2.4 GHz ethernet routers and not massively jam with you neighbors. The radio assigns a band of channels and actively listens for interference and hops around to avoid it. Yes, there can be interference, but normally with a few setting adjustments, they can sit in the same advertised box label frequency which has little bearing on the actual exact fequency and channels used. My point was I tried to link you to success stories to quell the myth that you cannot use the same advertized frequency for both video and telemetry. That's the beauty of the very technical engineering that has gone into the signals and protocols. Billions of dollars and research worldwide are now a direct benefit to you.
Also, I'm 99.999 percent sure I saw in a thread someone using 2.4GHz for both as well. The trick involved firing up the Video TX first, then the other data radio set. The reason was that yes, the video is a more traditional band radio centered around a frequency without hopping. Most if not all data radios are conforming to set set standards and do include automatic frquency hopping and thus, if you fire them up after the video, they sense the interference and map around it in the channel spectrum. It's what they were designed to do.
this all makes perfect sense, however I think I will stop worrying about the theory now and just try getting started using 2.4 GHz transmitter, if it doesn't work as i expect, I can still afford a 5.8GHz system (I ruled out all other frequencies now) and give it another try, selling the 2.4 GHz transmitter on ebay or whatever.
Any recommendations for a 2.4GHz TX / RX?